1. Field of the Invention
The present invention relates to a fastener driving tool for fastening a fastener such as a nail, rivet, or staple to a member to be fastened.
2. Description of the Related Art
In the related art, spring driven type fastener driving tools employing electric motors are well-known. This type of spring driven type fastener driving tool uses the drive power of an electric motor to push up a plunger urged by a spring in a direction from a lower dead point to an upper dead point in a fastening direction in resistance to urging force of the spring. A fastener such as a nail is then driven into a member to be fastened by an accelerated plunger as a result of the plunger that has been pushed up being released.
This kind of spring-driven fastener driving tool moves the plunger up to an upper dead point side using a power transmission mechanism that is a combination of an electric motor and reduction gears. The plunger is then released from the upper dead point side to the lower dead point side so as to drive in the nail (fastener). After this, it is then necessary for the spring-driven fastener driving tool to again cause the plunger to move back to the initial position using the drive force of the electric motor. Driving of the motor is then stopped at this prescribed position by a reverse rotation prevention mechanism such as a one-way clutch and the drive cycle is complete.
However, recently, it has been necessary for spring driven type fastener driving tools to increase the force with which the plunger is urged by the drive spring, i.e. the spring energy has been increased in order to increase the drive impact force to make it possible to drive in larger nails.
However, when the spring energy is made large, the spring driven-type fastener driving tool causes the plunger to move rapidly in resistance to the large urging force of the spring from the lower dead point side to the upper dead point side by making the rotational speed of the electric motor, i.e. the spring compression speed fast. It is therefore necessary to make the plunger stop at a prescribed position after driving. However, making the spring compression speed fast causes variation in the plunger stop position, i.e. the spring compression distance, due to the rotational inertia of the motor and the power transmission mechanism caused by changes in the mechanical loss of the power transmission mechanism overtime etc. Variations in the plunger stop position occurring in the drive cycle are then the cause of variation in the spring compression time occurring in the next drive cycle. This means that the spring compression time varies, the spring compression can therefore becomes longer, and the driving feeling and drive efficiency therefore deteriorate.
In order to resolve the above problems, it is an object of the present invention to provide a highly reliable spring drive method the fastener driving tool that is capable of suppressing variation in the stop position of a plunger and is capable of improving the feeling when driving.